GATA6 regulates HNF4 and is required for differentiation of visceral endoderm in the mouse embryo

GATA6 belongs to a family of zinc finger transcription factors that play im portant roles in transducing nuclear events that regulate cellular differen tiation and embryonic morphogenesis in vertebrate species. To examine the f unction of GATA6 during embryonic development, gene targeting was used to g enerate GATA6-deficient (GATA6(-/-)) ES cells and mice harboring a null mut ation in GATA6. Differentiated embryoid bodies derived from GATA6(-/-) ES c ells lack a covering layer of visceral endoderm and severely attenuate, or fail to express, genes encoding early and late endodermal markers, includin g HNF4, GATA4, rw-fetoprotein (AFP), and HNF3 beta. Homozygous GATA6(-/-) m ice died between embryonic day (E) 6.5 and E7.5 and exhibited a specific de fect in endoderm differentiation including severely down-regulated expressi on of GATA4 and absence of HNF4 gene expression. Moreover, widespread progr ammed cell death was observed within the embryonic ectoderm of GATA6-defici ent embryos, a finding also observed in HNF4-deficient embryos. Consistent with these data, forced expression of GATA6 activated the HNF4 promoter in nonendodermal cells. Finally, to examine the function of GATA6 during later embryonic development, GATA6(-/-)-C57BL/6 chimeric mice were generated, la cZ-tagged GATA6(-/-) ES cells contributed to all embryonic tissues with the exception of the endodermally derived bronchial epithelium. Taken together , these data suggest a model in which GATA6 lies upstream of HNF4 in a tran scriptional cascade that regulates differentiation of the visceral endoderm . In addition, these data demonstrate that GATA6 is required for establishm ent of the endodermally derived bronchial epithelium.